Foamed fireproofing composition and method

ABSTRACT

Disclosed are formulations adapted to form a foamed cementitious composition, the foamed cementitious composition itself, a method of forming a hydraulic binder foam, and a method of conveying and applying the resulting foam to a substrate. A pumpable cementitious slurry is formed, the slurry is mixed with a gas such as air, and is subjected to mechanically created turbulence to generate gas bubbles and create a foam, which preferably is stabilized by a foam stabilizing agent such as polyvinyl alcohol present in the slurry. The foam is then conveyed to a nozzle or other suitable dispense point from which it is applied, for example sprayed, preferably uniformly, onto a substrate to be coated. Prior to dispensing, a set accelerator is preferably injected, which causes the foam to gel, which in turn improves the hangability of the product on a substrate. The spray material adheres to the substrate and hardens to form an insulative coating on the substrate. Also disclosed are dry compositions comprising a hydratable cementitious binder, a mechanical foam stabilizing agent, and optionally a fibrous component, set retarder and air entraining agent, said composition providing, on the addition of water, gas and mechanical turbulence, a settable foam which is capable of spray application to a steel structural member and which, after spray application, is adherent to the member in the foamed state and after setting. The foam after setting, forms a fire and heat protective adherent coating on the member.

BACKGROUND OF THE INVENTION

[0001] In the course of erecting steel structures, a thick coating ofinorganic material is commonly applied to the metallic structuralelements to achieve a number of objectives including fire retardation,improved appearance and sound deadening. While several types offormulations have been applied for these purposes over the years bymeans of a variety of techniques, the most successful system so farconsists in spraying onto the steel surfaces settable aqueous mixescomposed essentially of calcined gypsum, a lightweight inorganicaggregate material such as exfoliated vermiculite or shredded expandedpolystyrene to lower the density of the mix, a mixture of fibrousmaterials such as a high wet bulking cellulose fiber and glass fiber,and an air entraining agent to render the wet mixture pumpable. Acomposition of this type is described by Bragg in U.S. Pat. Nos.3,719,573 and 3,839,059, along with the most desirable applicationtechnique, i.e., pumping the aqueous mix and spraying it directly ontothe steel in one layer. Such slurries are generally prepared at groundlevel and are pumped to the point of application, where they arespray-applied to the substrate. Often the point of application exceeds20 or 30 stories where high rise construction is involved. Accordingly,pumpability of the slurries is an important criterion in theirformulation and preparation. The slurries must be able to hold the largequantity of water that renders them capable of being pumped easily andto great heights, yet they must retain a consistency sufficient toprevent segregation or settling of ingredients and permit adequate yieldor coverage of the substrate at a given thickness. The coating mixesmust also adhere to the substrate, both in the slurried state duringapplication, and in the dried or “set” state after application. Inaddition, the mix must set without undue expansion or shrinkage thatcould result in the formation of cracks that would seriously deter fromthe insulative value of the dry coating.

[0002] In the conventional process, fireproofing mixes are transportedto the application site as dry mixtures and in a mixer an appropriateamount of water is added to form the pumpable slurry. The slurry ispumped from temporary holding equipment to the point of application.Where the components are pumped over distances, premature set-up canoccur prior to reaching the final destination. In addition, thepreparation and application processes may span many hours. Accordingly,the setting time of the mix is generally retarded by the inclusion ofset retarding agents to provide an acceptable field pot life. Inaddition, air-entraining agents such as alpha-olefin sulfonate andsodium lauryl sulfate are used to aid pumpability of the slurry.

[0003] U.S. Pat. No. 4,904,503 to Hilton et al. teaches thatacceleration of the setting time and also the “yield” of theaforedescribed pumped and sprayed fireproofing mixes is obtained byinjecting an acidic set accelerating agent such as alum into the slurryprior to spraying. The acid agent, prior to causing accelerated set,reacts with basic material such as calcium carbonate present in the mixto generate gas such as carbon dioxide. The evolved gas expands or foamsthe slurry which further reduces the density and increases the volume ofthe applied fireproofing after setting per given weight of dryfireproofing used. Such “chemically foamed”, “high yield” sprayfireproofing has been successfully commercialized around the world.

[0004] The “yield” or volume of applied fireproofing per weight of drymix is an important factor in the commercial success of the product. Thehigher the yield, the more coverage an applicator can obtain for a givenamount of formulation. Yield is generally calculated by methods known inthe art as board feet per dry weight of composition.

[0005] U.S. Pat. No. 3,963,507 discloses a foaming mortar containingspecific ratios of water-soluble, low-viscosity cellulose derivativessuch as methyl cellulose, ethyl methyl cellulose and hydroxyethyl methylcellulose; high-viscosity cellulose derivatives, and polyvinyl alcoholas a foaming accelerator.

[0006] U.S. Pat. No. 4,518,652 discloses a method for producing gypsumwallboard by producing a foam comprising polyvinyl alcohol and water,introducing the foam into an aqueous cementitious slurry, depositing theslurry between paper cover sheets, and allowing the slurry to set. Anemulsion of asphalt and wax can be added to the cementitious slurry toimpart water resistance.

[0007] U.S. Pat. No. 4,518,652 forms lightweight gypsum wallboard byincorporating pre-generated foams into gypsum slurries followed bysetting of the foam-slurry mix. The foam is formed by dissolvingpolyvinyl alcohol in water and placing it into a high shear foamingapparatus.

[0008] It would be desirable to produce a pumpable, low density, highyielding sprayable fireproofing composition that eliminates or reducesthe need for a lightweight aggregate.

[0009] It further would be desirable to produce a low density, highyielding, pumpable, sprayable fireproofing composition that can beeasily prepared at the site of the application without the need for highshear foaming devices and the like, and which upon application, resultsin excellent yields.

SUMMARY OF THE INVENTION

[0010] The present invention relates to a formulation adapted to form afoamed cementitious composition, the foamed cementitious compositionitself, a method of forming a hydraulic binder foam, and a method ofconveying and applying the resulting foam to a substrate. Morespecifically, a pumpable cementitious slurry is formed, the slurry ismixed with a gas such as air, and is subjected to mechanically createdturbulence to generate gas bubbles and create a foam, which preferablyis stabilized by a foam stabilizing agent such as polyvinyl alcoholpresent in the slurry. The foam is then conveyed to a nozzle or othersuitable dispense point from which it is applied, for example sprayed,preferably uniformly, onto a substrate to be coated. Prior todispensing, a set accelerator is preferably injected, which causes thefoam to gel, which in turn improves the hangability of the product on asubstrate. The spray material adheres to the substrate and hardens toform an insulative coating on the substrate. The particularly preferredcompositions are capable of providing a high yield of fireproofmg thatcan be applied to substrates at typical commercial application rates ofabout 1800 boardfeet/hour.

[0011] The present invention is also directed to a dry compositioncomprising a hydratable cementitious binder, a mechanical foamstabilizing agent, and optionally a fibrous component, set retarder andair entraining agent, said composition providing, on the addition ofwater, gas and mechanical turbulence, a settable foam which is capableof spray application to a steel structural member and which, after sprayapplication, is adherent to the member in the foamed state and aftersetting. The foam after setting, forms a fire and heat protectiveadherent coating on the member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is an electron microscope image of the microstructure of afoam in accordance with one embodiment of the present invention wherealuminum sulfate is injected into the foam;

[0013]FIG. 2 is an electron microscope image of the microstructure of afoam in accordance with one embodiment of the present invention wherealuminum sulfate is not injected into the foam;

[0014]FIG. 3 is a schematic representation of apparatus suitable formixing, foaming and conveying the components to a dispense point inaccordance with an embodiment of the present invention; and

[0015]FIG. 4 is a schematic representation of an air-separating and foamflow control enclosure in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Suitable hydraulic binders useful for the formation of acementitious slurry in the present invention include Portland cement,aluminous cement, pozzolanic cement, gunite, calcium sulfatehemi-hydrate (gypsum, both non-hydrated and hydrated Plaster of Paris),with gypsum being particularly preferred. Portland cement is known to bethe binder of choice where resistance to moisture is important or inhigh traffic areas where higher density (e.g., 15-30 pcf, more typically22-26 pcf) coatings are desired. While gypsum can be used in higherdensity applications, it is usually used for light density (about 5-19pcf, preferably about 10-15 pcf) compositions. Preferably the binder isused in an amount of about 10 to about 98% by weight, more preferablyabout 90 to about 95% by weight. Preferably the hydraulic binder isprovided in a finely divided dry powder form.

[0017] The term “foam” is used herein to mean a group of bubblesseparated from one another by thin films, the aggregation having afinite static life sufficiently long to allow for conveying and sprayingof the foam in accordance with the present invention.

[0018] In order to stabilize the foam mechanically formed in accordancewith the present invention, surfactants, protein compounds, and/orhydrophilic compounds or polymers that are soluble, miscible ordispersible in water are suitable. The preferred foam stabilizing agentis polyvinyl alcohol, most preferably powdered polyvinyl alcohol. Theamount of polyvinyl alcohol used as a foam stabilizing agent ispreferably in an amount of from about 1% to 12% inclusive by mass ofwater, more preferably about 2% to 10% inclusive, even more preferablyabout 2% to 8%, most preferably about 2-3% in order to ultimatelyproduce a foam of the desired density. The viscosity of the polyvinylalcohol used affects the volume increase of the foamed composition fromthe unfoamed state. Preferred polyvinyl alcohols are partiallyhydrolyzed grades with a degree of hydrolysis mol % in the range of 79%to 90%, preferably about 88%, with an ester value mg KOH/g of 140, andresidual acetyl content weight percent of 10.7. Examples of suitablepolyvinyl alcohols are the Mowiol grade sold by Clarient, 4/88 throughto 40/88, which at 20° C. and at a 5% concentration in water, each haveviscosities of 8 Pa.s for 4/88, 9 mPa.s for 5/88, 12 mPa.s for 8/88, 55mPa.s for 18/88 (which is particularly preferred), 75 mPa.s for 23/88and 100 mPa.s for 40/88; and Celanese Celvol 523S and 523 SF. It is mostpreferable that the polyvinyl alcohol be used in the form of a powder.The powder must be comprised of particles sufficiently small to ensurethat the polyvinyl alcohol readily dissolves in water. Powderedpolyvinyl alcohols having particles averaging from 80 to 400 micronshave been found to be suitable. Those skilled in the art can readilydetermine which commercially available polyvinyl alcohol powders inaddition to the foregoing are suitable.

[0019] Other suitable foam stabilizers include fluoro surfactants suchas those commercially available from duPont, including Zonyl FS300,which is a general-purpose non-ionic fluoro surfactant free of organicsolvents, unaffected by hard water or pH, with a large capacity to wetout. These may be used in an amount of from about 0.005% to about 0.5%inclusive by mass of water. Suitable protein compounds includehydrolyzed protein based concentrates. Protein compounds may be used inan amount of from about 2% to about 5% inclusive by mass of water.Suitable hydrophilic compounds or polymers include modified starches,natural carbohydrates such as gums or seaweed colloids, semi-syntheticpolymers such as the cellulose ethers, hydrogels such as the homo- andco-polymer derivatives of acrylic and methacrylic acid, or thepolyacrylamide polyacrylate co-polymers, and dispersions such aspolyvinyl acetate and styrenated acrylics.

[0020] In contrast to the chemically foamed, pumped and sprayedfireproofing described in the aforementioned U.S. Pat. No. 4,904,503 andpresently used in commercial practice, the foams of the presentinvention are mechanically created. Foam generation apparatus such ashigh shear mixers known in the board-making art can be used. However, ithas been found that such device are unnecessary and that the mechanicalcreation of turbulence effective to generate gas bubbles and therebyfoam the slurry can be carried out in the tubing or hosingconventionally used in present pump and spray fireproofmg applications,which tubing or hosing is also used to convey the resulting foam to adispense point such as a nozzle for ultimate spray application to thesubstrate. The gas, preferably compressed air, preferably is introducedinto the hose or tube in which the slurry is resident, such as byinjection. In one embodiment of the present invention, the location ofthe gas introduction into the hose or tubing is near the dispense point,since it has been found that as the hose or tube length increases afterthe point of gas introduction, the longer it takes for the foam to reachsteady state (defined as capable of being dispensed from the hose at auniform rate without large pulses of gas). It is desirable that steadystate be reached, otherwise the foam is ejected from the dispense pointas plugs rather than a uniform spray. Pulsed dispense makes it difficultto uniformly apply the foam to the substrate, as the pulses of gas tendto “blow” the product off of the substrate as fast as it can be sprayedonto the substrate. In addition, locating the gas introductionrelatively close to the point of application minimizes the length ofhose through which the foam needs to be conveyed.

[0021] The density of the foam produced is a function of the rate offlow of the slurry as well as the length and diameter of the hose ortubing, as well as the gas pressure and gas volume (cfm) injected intothe foam, and the residence time of the slurry (and foam) in the hose ortube. Those skilled in the art can adjust the foregoing parameters toachieve the desired final density of the product. For example, onesuitable system uses a 50 foot hose having a diameter of ¾ inch and airinjection at a rate of 26 cfm at 70 psi. If the hose or residence timeof the composition in the hose is too short, insufficient foaming willoccur. If the hose or residence time of the composition in the hose istoo long, steady-state will not be realized and the composition willform plugs which “spit” from the exit and cannot be readilyspray-applied to the substrate in a uniform manner as mentioned above.The objective is to provide a hose of sufficient length and diameter sothat the composition entering the hose in a slurried state can be foamedwith gas and reach steady-state prior to the composition exiting thehose. Those skilled in the art balance the flow rate as well as thelength and diameter of the hose with the gas pressure and gas volumebeing injected into the hose to achieve a desired foam consistency anddensity. It has been found that for a given hose diameter and a givenair pressure, shorter hoses result in the foamed product reachingequilibrium or steady-state faster than longer length tubes. Forexample, the foam reached equilibrium in a 25 foot hose having a 0.5inch diameter in 30 seconds compared to more than 300 seconds for a 0.5inch diameter hose 150 feet long. Similarly, foams in hoses 25 and 50feet long with diameters of ¾ inch reached equilibrium immediately,whereas lengths of 100 feet at a diamter of ¾ inches took 55 seconds and150 feet with the same diameter took more than 300 seconds.

[0022] Suitable hose or tubing lengths include 15 to 150 feet, withdiameters including ½″, ⅝″, ¾″and 1 inch. Shorter length hoses allow theproduct to reach equilibrium or steady state faster than longer lengths.For a given formulation, the density of the product was the sameregardless of whether the tube was coiled or laid in straight line. Anadvantage of the present invention is that the fireproofing can beapplied using lighter weight hoses than those conventionally used,easing the burden on the applicator.

[0023] The compositions of the present invention can include a fibrouscomponent. The fibrous component can be either organic or inorganic.Preferably, the fibrous component is a mixture of a high wet bulkingorganic fiber, preferably cellulose fiber as described in U.S. Pat. Nos.3,719,513 and 3,839,059, and an inorganic fiber which providesreinforcement, preferably steel or glass fiber. Polymeric reinforcingfibers such as polypropylene fibers also can be used. Other suitablecomponents include silica, diatomaceous earth, expanded perlite,exfoliated vermiculite, shredded expanded polystyrene, alumina, grog,colloidal silica, ceramic fibers, mineral fibers and combinationsthereof. The total amount of the fibrous component in the composition ispreferably in the range of about 0% to about 40% by weight. Aparticularly preferred composition comprises about 4% to 10% by weightof high wet bulking cellulosic fiber and about 0.0% to about 1% byweight of glass fiber, with about 1% cellulosic fiber and about 0.5 %glass fiber being especially preferred. Other optional additives includemethyl cellulose or other suitable thickeners or air stabilizers knownto those skilled in the art, in an amount from about 0.1 to about 5%,chemical air entrainers in an amount of from about 0.1 to about 3%;polyvinyl acetate in an amount of from 0 to about 5%; clay in an amountof from about 1% to about 5%; gas generants such as calcium carbonate inan amount of about 0% to about 5%; and a biocide to inhibit bacterialformation. Where possible, the optional components are added in the drystate to the hydraulic binder in order to form a slurry precursor oradmixture for convenience.

[0024] Since the compositions of the present invention are typicallytransported to the application site as dry mixtures and are formed intoslurries upon the addition of the appropriate amount of water, thepreparation and application process may span many hours or even days,and thus the setting time of the mix is generally heavily retarded toprovide an acceptable field “pot life”. This retarding contradicts thedesired quick setting time upon application to the ultimate substrate,and thus a delicate balance of retarding and accelerating is difficultto achieve. Were the mixture to set prematurely, it would be renderednon-pumpable and useless for the intended application. Accordingly, aretarder is preferably used to delay the set time of the composition toavoid premature set. Suitable retarders are conventional in the art, andinclude maleic anhydride, used in an amount of 0.1% to 0.75% inclusiveby mass of the hydraulic binder, sodium polyacrylate and polyacrylicblend. The preferred retarder is the standard proteineous retarder usedin the industry, such as that commercially available under the nameGoldbond High Strength Retarder. The retarder is preferably added to thehydraulic binder in the dry state for convenience.

[0025] Accelerators can be added to the cementitious composition inorder to decrease the set time upon a structure. Any set acceleratingagent capable of satisfactorily offsetting the retardation of the slurrywithin the desired time period without deleteriously effecting the sameor the substrate which is the subject of the application can be used.For most commercial applications, the type and amount of accelerator isthat which rapidly converts the setting time from about 4 to about 20hours to about 5 to 15 minutes. The amount required to provide such asetting time will vary depending upon the accelerator and the type andamount of retarder and binder. Generally, an amount in the range ofabout 0.1% to 20% by weight of dry accelerator based upon the weight ofdry fireproofing is used, with 1-5% being preferred. Suitableaccelerators are those known to accelerate the set of the hydraulicbinder employed. For gypsum based hydraulic binders, suitableaccelerators include aluminum sulfate, aluminum nitrate, ferric nitrate,ferric sulfate, ferric chloride, ferrous sulfate, potassium sulfate,sulfuric acid, sodium carbonate, sodium bicarbonate and acetic acid.Aluminum sulfate is a preferred accelerator. It can be used as asolution. Where Portland cement is the hydraulic binder, conventionalset accelerators can be used such as calcium choride, calcium formate,calcium nitrate, alkali aluminates, and silicates such as water glass.

[0026] It has further been found that the introduction of aluminumsulfate into the foamed composition can be used to control the stabilityof the foam by modifying the microstructure of the formulation,particularly in compositions comprising polyvinyl alcohol as the foamstabilizing agent and calcium sulfate hemihydrate as the hydraulicbinder. Specifically, foams that are “more stable” produce finerstructures, while foams that are “less stable” produce coarserstructures. The size of the voids or pores formed thus can be critical,and can be controlled by controlling the rate of reaction of the calciumsulfate hemihydrate with water to form calcium sulfate dihydrate.Aluminum sulfate can be used to accelerate this reaction, therebycontrolling the stability of the resulting foam such as by producingfoam having a finer microstructure. In essence, introduction of thealuminum sulfate into the foam reacts with the binder and causes it toset, thereby “freezing” the microstructure of the foam. Preferably theintroduction of aluminum sulfate is introduced near or at the nozzleused to spray the foam onto the substrate, such as by using a nozzle asdisclosed in U.S. Pat. No. 4,904,503, the disclosure of which is herebyincorporated by reference.

[0027] The dramatic results achieved in the microstructure of the foamupon the addition of aluminum sulfate can be seen with reference toFIGS. 1-2. FIGS. 1 and 2 are foams prepared under identical conditionsexcept that the foam in FIG. 1 was injected with alum at the spraynozzle, whereas the foam of FIG. 2 received no alum injection. Theresulting foam of FIG. 1 shows a finer microstructure than that of FIG.2.

[0028] The introduction of set accelerator, such as alum, in a mixturethat includes a foam stabilizer, such as polyvinyl alcohol and anair-entraining agent such as alpha olefin sulfonate, also causes thefoam to “gel”. The consistency of the foam changes from a “shavingcream” consistency to a “sticky” mass upon the introduction of setaccelerator and its distribution into the foam. Gel formation enhancesthe ability of the product to remain or “hang” on a substrate,particularly a steel beam or the like, before and during the settingtime. The addition of a basic substance such as calcium carbonateenhances the gelling. The set accelerator thus serves to both form thegel, and then to accelerate the setting of the hydraulic binder.

[0029] With reference to FIG. 3, to form the cementitious slurry inaccordance with one embodiment of the present invention, the hydraulicbinder, set retarder, foam stabilizing agent and water are mixed in ahopper 112, together with optional components such as the fibrousmaterial. A lightweight aggregate is not needed in view of the inherentlightweight provided by the foaming. The order of addition of thevarious components is not critical. Preferably the mixing is carried outat or near the site of application, both to avoid premature setup of thecomposition and to limit the distance the slurry has to be conveyed onceformed. Dry material, such as the hydraulic binder, retarder, and otheroptional components, are mixed in a hopper 112 or other suitable mixingvessel. Water and foam stabilizing agent are added, together orseparately, to form the cementitious slurry. In a preferred embodimentof the present invention, where powdered polyvinyl alcohol is the foamstabilizing agent, the powdered polyvinyl alcohol is mixed with thehydraulic binder, retarder and optional components in the dry state.Water is then added to the dry mixture to form a pumpable cementitiousslurry. The slurry thus formed is conveyed, preferably by pumping withpump auger 110, to a hose or tubing 100 as discussed above. Conveyanceof the slurry should be at commercially feasible rates, generally about1800 board feet/hour. Variable speed rotor stator pumps such as thePutzmeister S-5 are suitable for this purpose.

[0030] The most preferred dry mix formulation in accordance with thepresent invention that, upon addition of water, forms a slurry,comprises 90-95% stucco, 1-3% powdered PVA (Mowiol 18-88 G-2 powder), 1%cellulosic fibers, 0.5% glass fibers, 0-2% calcium carbonate, 0.25%alpha-olefin sulfonate, 0.1-0.3% retarder, and 0-2% Portland cement.This formulation, particularly with the inclusion of calcium carbonate,upon the addition of water the mechanical formation of foam, and the setacceleration by alum addition at or near the spray nozzle, results in alow density product (dry density 9.3 pcf) exhibiting improvedhangability (1-1.5 inches thick on a steel substrate) at a low cost. Asmall amount of basic substance such as Portland cement can be added tominimize or prevent any significant carbon dioxide generation caused bythe alum reacting with carbonate. The Portland cement raises the pH ofthe mix and inhibits the reaction of the acidic accelerator with base.The above preferences may vary depending upon the desired final densityof the product.

[0031] Gas, preferably air, is introduced, preferably by injection, intothe hose with a pipe or tube 21 in communication with a compressor 22.Sufficient gas is introduced to foam the slurry and to convey theresulting foam towards the nozzle 10. Those skilled in the art willappreciate that this introduction of air to mechanically foam the slurryand convey the resulting foam is different from the conventional use ofchemical air-entraining agents to entrain air in an open system toimprove pumpability. Although the introduction of gas at a singlelocation is preferred, gas can be introduced at several locations alongthe hose, if desired.

[0032] In order to further reduce or eliminate pulsing that can occur asthe foam is sprayed from the hose, the pressure in the hose can becontrolled a number of different ways. Controlling the pressure in thehose provides a dampening effect to the spraying operation. Pressurealso can be used to control the rate of spray out of the nozzle 10. Inaddition, the final density of the product can be controlled usingpressure. In its simplest form, a pressure relief valve or the like canbe incorporated in the hose in order to vent gas (air) from the hose tocontrol the pressure in the hose. In another more preferred embodiment,an air-separating and foam flow control enclosure 12 defining anexpansive volume (relative to the hose) can be placed in line, wherebythe foam in the hose is fed into the inlet of the enclosure and isforced out an outlet in the enclosure to a further length of hoseleading to the nozzle. The enclosure can have a controlled vent in orderto regulate the pressure therein. The mass flow rate into the enclosureis controlled by the pump pumping the slurry into the hose, and the massflow rate out of the enclosure is controlled by the pressure in theenclosure. The velocity of the gas used to convey the foam in the hoseis high, which makes it difficult to effectively spray the foam. Theenclosure 12 allows the gas that is conveying the foam to separate fromthe foam, and allows control of the flow rate of the foam independent ofthat velocity.

[0033] Turning now to FIG. 4, there is shown such an enclosure 12 havingan inlet 14 communicating with the hose conveying the foam and an outlet16 spaced from the inlet 12. The foam being conveyed by compressed airin the hose enters the enclosure 12 at the inlet 14. As the foam/airmixture enters the enclosure 12, the excess (i.e., conveying) airseparates from the foam and the foam falls to the bottom of theenclosure 12 where it is forced out the outlet 16 by the pressure in theenclosure 12 into a further length of hose 18 and finally out nozzle 10.An air vent 20 in communication with a valve 22 such as a gate valveallows the pressure in the enclosure 12 to be controlled to a desirablelevel. The pressure can be controlled manually or automatically. Apressure gauge 19 displays the enclosure 12 pressure. Suitable pressuresin the enclosure 12 can be is controlled to between about 10 and about65 psi, depending upon the flow rate desired and the exiting hosediameter and length. A pressure of about 40 psi. has been found to beparticularly suitable in one application. This has been found to besufficient pressure to cause the foam to be forced out of the outlet 16and travel through the hose 18 and be sprayed out of nozzle 10 at anacceptable rate. An added advantage is that because the foam is underpressure, additional air entrainment occurs since more air is forcedinto the foam. The result is an even lower density product compared toidentical formulations sprayed absent the enclosure 12.

[0034] Preferably the length of hose from the outlet 16 of the enclosure12 to the nozzle 10 is from about 15 to 30 feet. The diameter of thehose 18 should be as small as possible in order to provide hoseflexibility for ease of application. However, as the diameter decreases,more pressure is needed to convey the foam through the hose, and as thepressure increases, the spray tends to exit the nozzle faster, which maybe undesirable. Diameters of from 1 to 1.5 inches have been found to besuitable, with a hose length of about 25 feet being especially preferredin order to ensure that the enclosure 12 does not interfere with theapplicator. For example, where the applicator is operating in ahigh-rise building, preferably the enclosure 12 is located on the samefloor as the applicator, whereas the mixing and pumping equipment formixing and pumping the slurry is generally located on the ground floorof the building.

[0035] In the present system, the amount of air that is contained in theproduct is substantially greater than conventional pump and sprayfireproofing compositions. In general, the amount of air contained inthe product of the present invention is at least about twice the amountcontained in conventional pump and spray fireproofing products, and ispreferably at least about 4 times that amount.

EXAMPLES 1-6

[0036] In all cases, all of the materials listed in Table 1 except forwater were dry blended for 3 minutes to have a uniform mixture. Thismixture was then added to a standard paddle mixer and the water wasadded. This combination was mixed for 2 minutes. The slurry produced waspoured into the pump hopper of a rotor/stator type pump (PutzmeisterS-5). The slurry was then pumped to another location, where air wasinjected into the slurry that was in the hose. This air injection turnedthe slurry into a foam in the 30′ of ¾″ foaming hose.

[0037] In Formulas 1 and 2 in Table 1, the foam entered anair-separating and foam flow control enclosure that was pressurized to37 psi. The foam then was forced out of the enclosure and passed through25′ of 1″ hose and a standard spray nozzle. Alum was injected into thefoam as the foam was passing through the spray nozzle.

[0038] In Formulas 3, 4, 5 and 6, the air-separating and foam flowcontrol enclosure was not used. A standard spray nozzle was attacheddirectly to the end of the 30′ of ¾″ hose in which the foaming wastaking place (see the end of the paragraph above). As in cases 1 and 2,alum was injected into the foam as the foam was passing through thespray nozzle.

[0039] Table 1 shows the final density of the products. Formula 6 is ahigh density product containing Portland cement as the primary hydraulicbinder. TABLE 1 Formula 1 Formula 2 Formula 3 Formula 4 Formula 5Formula 6 Materials (pounds) (pounds) (pounds) (pounds) (pounds)(pounds) Polyvinyl alcohol 2 3 3 4 2 3.3 Stucco 94.15 92.95 93.85 91.8593.85 15.9 Proteineous retarder 0.1 0.3 0.3 0.3 0.3 1.4 Cellulosic fiber1 1 1 1 1 1.1 Glass fiber 0.5 0.5 0.5 0.5 0.5 0.5 Portland cement 2 X XX X 77.8 Air entrainment 0.25 0.25 0.35 0.35 0.35 X (alpha olefinsulfonate) calcium carbonate X 2 1 2 2 X Water 100 100 100 100 100 90foaming air psi 98 100 100 100 97 38 Foamimg air cfm 37 37 48 42 60 27slurry rate (pounds/hour) 960 1216 1024 1024 1024 125 alum addition 3 23 1 3 5 final density (pcf) 12.4 9.9 9.2 7.9 11.4 22.9

EXAMPLE 7

[0040] In an example of a pumped and sprayed foam of the invention,suitable for use in “shotcrete” applications (sealing the walls oftunnels and mines), the stucco and retarder used in Formula 6 of Table 1is replaced by additional Portland cement. The cellulose and glass fiberused in Formula 6 is replaced by conventional steel fiber used inshotcrete applications, and the resulting formula is processed as in theforegoing Examples 1-6, except that sodium aluminate is used as the setaccelerator in place of alum.

What is claimed is:
 1. A method of producing a hydraulic binder foam,said method comprising: forming a slurry comprising a hydraulic binder,a foam stabilizing agent and water; conveying said slurry to a length ofhose; introducing an amount of gas into said slurry in said length ofhose at a flow rate and pressure sufficient to cause said slurry to foamand to convey said foam through said length of hose.
 2. The method ofclaim 1, wherein said hydraulic binder is selected from the groupconsisting of Portland cement, gypsum, and combinations of Portlandcement and gypusm.
 3. The method of claim 1, wherein said hydraulicbinder is gypsum.
 4. The method of claim 1 or 3, wherein said foamstabilizing agent is polyvinyl alcohol.
 5. The method of claim 1,wherein said slurry further comprises a set retarder.
 6. The method ofclaim 1, further comprising introducing a set accelerator into saidfoam.
 7. The method of claim 1, further comprising introducing aluminumsulfate into said foam.
 8. The method of claim 7, further comprisingspray applying said foam to a substrate and allowing it to harden onsaid substrate.
 9. The method of claim 1, wherein said hydraulic binderis calcium sulfate hemihydrate, said foam stabilizing agent is polyvinylalcohol, and further comprising introducing aluminum sulfate into saidfoam in said length of hosing.
 10. A method of forming a stabilized foameffective for spray application, comprising: mixing a formulationcomprising calcium sulfate hemihydrate, polyvinyl alcohol, a setretarder; and a sufficient amount of water to react with said calciumsulfate hemihydrate to form calcium sulfate dihydrate and cause said mixto form a pumpable slurry; conveying said slurry to a length of hose;introducing air into said slurry in said length of hose to createturbulence and mechanically form a foam; conveying said foam throughsaid hose; and introducing aluminum sulfate into said foam to acceleratethe formation of calcium sulfate dihydrate.
 11. The method of claim 10,further comprising spray applying said foam onto a substrate.
 12. Afireproofing composition adapted to be spray applied to a steelsubstrate, comprising a hydraulic binder, a foam stabilizing agent and aset retarder, said composition, when mixed with water and gas, providinga settable foam capable of spray application to a steel substrate andwhich, after spray application is adherent to said substrate in thefoamed state and after setting.